This example clarifies the description:
#mesh of a table
MESH "board" dimension 3 ElemType Triangle  Nnode 3
# color 127 127 0
Coordinates
# node number   coordinate_x  coordinate_y  coordinate_z
    1             -5              3             -3
    2             -5              3              0
    3             -5              0              0
    4             -2              2              0
    5       -1.66667              3              0
    6             -5             -3             -3
    7             -2             -2              0
    8              0              0              0
    9             -5             -3              0
   10        1.66667              3              0
   11       -1.66667             -3              0
   12              2              2              0
   13              2             -2              0
   14        1.66667             -3              0
   15              5              3             -3
   16              5              3              0
   17              5              0              0
   18              5             -3             -3
   19              5             -3              0
End Coordinates

#we put both material in the same MESH, 
#but they could be separated into two MESH

Elements
# element  node_1   node_2  node_3 material_number
    5         19      17      13     3
    6          3       9       7     3
    7          2       3       4     3
    8         17      16      12     3
    9         12      16      10     3
   10         12      10       4     3
   11          7       9      11     3
   12          7      11      13     3
   13          2       4       5     3
   14          5       4      10     3
   15         19      13      14     3
   16         14      13      11     3
   17          3       7       4     3
   18         17      12      13     3
   19         13      12       8     4
   20         13       8       7     4
   21          7       8       4     4
   22          4       8      12     4
End Elements

MESH    dimension 3 ElemType Line Nnode 2
Coordinates
#no coordinates then they are already in the first MESH
End Coordinates

Elements
# element  node_1   node_2 material_number
    1          9       6     5
    2         19      18     5
    3         16      15     5
    4          2       1     5
End Elements
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